In order to facilitate the dispatching of emergency services such as provided by police, fire departments, ambulances and the like, many urban communities have instituted a universal telephone number, usually 9-1-1, for reporting emergencies of any kind. When the 9-1-1 number is dialed, the call is routed to a central emergency center for voice communication between an emergency operator and the caller. The operator must ascertain from the conversation the caller's location and nature of the emergency. The operator then contacts the appropriate emergency service agency either verbally or by routing the call directly to the agency by means such as are disclosed in U.S. Pat. No. 4,052,569 issued to Pirnie. The nature of the emergency can usually be quickly communicated, but the caller's location may either be unknown to the caller or difficult to describe. A need exists, therefore, for emergency call answering systems which enable a caller's location to be quickly ascertained so that the appropriate emergency service may be quickly dispatched to that location.
One of the best ways for transmitting location information is by means of a visual display. For example, U.S. Pat. No. 4,558,300 issued to Goldman discloses an electronic map for selectively displaying building floor plans indicating a plurality of stations with paths connecting the different stations. By selecting a particular station at a keyboard, a pathway extending from the particular station to the location of the keyboard is visually displayed. Similarly, U.S. Pat. No. 4,421,645 issued to Carroll discloses an alarm system using either fire or burglar alarm detectors which communicate with a micro-computer. When one of the detectors is actuated, the micro-computer having stored therein the position of each detector and the floor plan of each floor of the building communicates that information over telephone lines to the nearest fire station or central monitoring station.
Existing telephone networks are designed such that information containing the telephone number of the calling party is automatically transmitted to a receiving party. This feature called Automatic Number Identification or ANI is utilized by the system disclosed in U.S. Pat. No. 3,881,060 issued to Connell et al. which is hereby incorporated by reference into the present specification. That system utilizes the telephone number of the calling party dialing 911 to automatically route the call to one of a plurality of central receiving stations. Similarly, the emergency telephone system of Mountain Bell in Phoenix, Ariz., as described in a Nov. 11, 1985, issued of Telephony, routes emergency calls to a central receiving station where a video screen shows to the operator the telephone number of the calling party as well as the name and address assigned to that phone number. A similar system of Continental Telephone Company in Virginia is described in the Feb. 24, 1986, issue of Telephony.